RE: Downgrade from RAID6 to RAID5

+1

Our SSD, Raid Controllers, and EXP24S exceeded the price of the rest of the 8205-E6C.
However, the performance was worth it.

Paul

-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Justin Taylor
Sent: Friday, November 24, 2017 1:37 PM
To: Midrange Systems Technical Discussion
Subject: Re: Downgrade from RAID6 to RAID5

FWIW, we have an 8202-E4B and a few years back we looked at adding external disks. Our BP quoted $30K, so I didn't bother to look at the specs.



________________________________
From: DrFranken <midrange@xxxxxxxxxxxx>
Sent: Friday, November 24, 2017 9:21 AM
To: Midrange Systems Technical Discussion; Don Brown
Subject: Re: Downgrade from RAID6 to RAID5

Sounds like a 4-core machine? So an expansion drawer is not an option in that case.

We have had good success adding the internal RAID card with the four credit card sized 177GB SSDs, it takes 2 slots but you can also add an 'upper deck' which is four PCIe slots above the power supplies. Me, I would mirror those drives as those particular RAID adapters do not have write cache.

Once installed you would tag your most popular files with *SSD and you get both space and performance.

Advantage:
EASY to install and at no time are you unprotected.
Supported configuration.
Drives and cards readily available at reasonable prices.

Disadvantage:
They are SSD so you need to add to maintenance or self maintain by simply buying 1 or 2 extra SSDs. To date we have not seen many of these units fail but they are getting older.
You MUST take the machine down to do a maintenance on them since the cover comes off.

As to directly addressing the RAID6 to RAID5 migration, others have mentioned the full save requirement (not to do the move but to assure your data doesn't go away) and the long time required to unstripe and restripe.

Performance improvement is there yes as you also remove some reads along with the extra writes but won't rock your world.

- Larry "DrFranken" Bolhuis

www.Frankeni.com<http://www.Frankeni.com>
www.iDevCloud.com<http://www.iDevCloud.com> - Personal Development IBM i timeshare service.
www.iInTheCloud.com<http://www.iInTheCloud.com> - Commercial IBM i Cloud Hosting.

On 11/24/2017 1:53 AM, Don Brown wrote:

Hi All,

Long story short.

Have a system at 7.3 with 6 x 139GB spinning disks RAID6 and a disk
write performance issue.

As RAID6 will require three writes to update all striping and RAID5
will need two theoretically converting from RAID6 to RAID5 should
provide a performance increase ?

There is no space for additional drives in this system - Mirrored pair
are used in Asp02

SSD's is not an option because both IBM and IBM remarketing both do
not have any of the required drives for this model 8202-E4B

We are considering second hand SSD's but not a preferred option.

Has anyone changed the RAID configuration from 6 to 5 and have any
comments on the process ?

Thanks
Don Brown

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